Here's #44! Click here for the master list!
Tales of the New Teen Titans #44
This one is pretty tough, because what you have here is the introduction of two fairly notable characters and simply the re-naming of another hero (while also, yes, the first appearance of another character, but I'm sorry Jericho fans, he isn't that noteworthy).
However, all said and done, I think the sidekick of Batman, Dick Grayson, becoming a new character, Nightwing, is more significant than the Wasp appearing in Tales to Astonish #44 (interesting that they're both Tales issues!) and Gorgon appearing in Fantastic Four #44 (which is less about Gorgon appearing as it is the first appearance of the Inhumans, kinda).
But really, this issue, which was the penultimate part of the Judas Contract, is just a slightly larger piece of comic book history than those issues, as the New Teen Titans by Marv Wolfman and George Perez was one of the highest-selling comic books of the early 80s, this was perhaps their most famous storyline, and it involved Dick Grayson, one of the most famous comic book characters in all of comics.
So I'm pretty confident in saying that this was the most notable #44 out there.
Still, Tales to Astonish #44 and Fantastic Four #44 are notable runners-up, as well as strong issues of Sandman, Swamp Thing, Doom Patrol and Amazing Spider-Man.
Any other good #44s?